Microbial desulfurization of coal has been perfected as shown by such disclosures as U.S. Pat. No. 4,456,688, Dugan et al and the publications cited therein. This disclosure concerning the steps of microbial treatment is herein incorporated by reference in regard to how to treat a sample of coal to desulfurize same with a mircoorganism. Living bacteria or microorganisms act as oxidation catalyst to promote the oxidation of insoluble metallic sulfide to soluble sulfate which is then transferred to an aqueous phase thereby extracting same from the solid particles of coal. In this manner, microbiological treatment of a ground coal will reduce sulfur content to a tolerable environmental level. Such microorganisms have been mixed with acid tolerant heterotrophs to advantageously desulfurize coal as taught in Dugan et al. The microorganisms exemplified by Dugan et al are acid tolerant Thiobacilli. These include T.thiooxidans, T.ferrooxidans, T.acidophilus and T.denitrificans.
In European patent application 126,443 (application No. 84105629.4) microorganisms capable of reducing the sulfur content in coal are obtained by growing the microorganisms in soil enriched with sulfur compounds. Contact of the aqueous coal slurry with the produced microorganism provides a coal having reduced organic sulfur content. Illustrative of other processes wherein microorganisms chosen from an acidophilic groups have been utilized to desulfurize coal are exemplified by U.S. Pat. No. 2,829,964. Other processes which employ Thiobacillus ferroxidans are exemplified by U.S. Pat. Nos. 3,218,252, 3,266,889 and 3,305,353, all of the teachings of which are herein incorporated by reference. The microorganisms exemplified in European patent 126,443 were deposited with the American Type Culture Collection (ATCC) with an accession number ATCC39,327 and which can be utilized in the desulfurizing step of this invention. This disclosure thus provides a ready access to microorganisms which will reproduce themselves in situ at an economically attractive rate.
Microorganisms can be suitable for different types of coal. In U.S. Pat. No. 3,796,308, McIlhinney et al, a process is described for upgrading coal ores containing inorganic sulfides by action of bacteria from the group of Thiobacillus ferrobacillus in an aqueous slurry. It was determined that by allowing an oxidizing bacteria to act only on the surface of the ore or coal that there is an alteration of the inorganic metal compound (pyrite) to a hydrophilic form, which thereby accelerates mineral interface separation. This achieves more efficient pyrite liberation from the coal. The process essentially comprises wet grinding to aid release of fine particles of metal sulfides and subjecting an aqueous mixture containing the ground material to action of an inorganic sulfide oxidizing bacteria to render the surface of the solids hydrophilic. The beneficiated ores are substantially free of the sulfur impurities. Microorganisms that can be employed for coal ores containing organic sulfides include Australian patent 29,597/84 (AU 8429597) wherein a pure culture of mutant Pseudomonas is taught as being useful to remove organic sulfur compounds from coal. The ATCC number for these mutants is 39,381 and they are likewise feasible bacteria for use in this invention when it is desired to treat coals having sulfur compounds of organic origin.
This invention concerns the combination of any viable microorganism desulfurization of coal in combination with concoction of a coal-water mixture. A leader in the field of formulating coal water admixtures is Occidental Petroleum Corporation. One publication of this company teaches how to use and how to make particular coal water mixtures. This publication entitled "Coal-Water Mixture Technology" is attached and herein incorporated by reference to this application. In the June 27, 1983 edition of Chemical Engineering at page 14, disclosure is made of various coal-water slurries and their adaptation to certain power plants. All of the above references fail to suggest combination of microorganism desulfurization technology with coal water mixture to prepare coal particles having a sulfur content of less than 1% by weight for economic and clean coal combustion.